Carrier frequency system



.March 1.0,-1942. A. wlEssNER ETAL K 2,276,132.

CARRIER FREQUENCY SYSTEM A Filed July 19, 19:59

, @Ef/170% i Patented Mar. 10, 1942 2,276,132 CARRIER FREQUENCY SYSTEM Alfred Wiessner and Herbert Ntz, Berlin, Germany, assignors to C. Lorenz Aktiengesellschaft, Berlin-Tempelhof, Germany, a company Application July 19, 1939, Serial No. 285,238 In Germany July 25, 1938 1 Claim.

In the development of multi-channel carrier frequency systems it has been found convenient to employ a modulation by steps if the low-frequency bands are to be displaced into a higher frequency range, the modulation being such that all of the low-frequency bands are for the rst modulated with the same carrier frequency, such as 6 to 10 kilo cycles per second, in order to be displaced by a second modulating step into a higher frequency range. In the case of multiband systems it is of advantage to use a third modulating stage. This method results in a simplification of the well known assembling filters.

The invention deals with carrier frequency systems of this kind, that is, systems of the multi-channel type which involve the use of a multi-stage modulating method, and has for its object to interconnect the terminal toll exchange thereof and of the respective subscribers telephone station in a manner to abolish the split connection customarily provided in this terminal toll exchange and subscribers station and thereby to avoid a reflux caused by an imperfection of the balancing or simulation device.

For effecting the two-path intercommunication of subscribers it has been proposed to employ in the direction from the toll exchange to the subscribers telephone station a carrier frequency which is modulated in accordance with the single-side band or intermediate-band method and is demodulated in the subscribers station, being then conveyed here to the telephone receiver. In the direction from the microphone of the telephone station to the toll exchange the low-frequency band is used.

For the transition from the talking channels of a multi-band system to two-path intercommunicaticn it is under the invention proposed to proceed as follows: In the talking direction from the remote end of this system the speech is not demodulated in a manner to obtain the lowfrequency band, but the Side band originating in the last modulating stage but one, .is supplied with the carrierirequency necessary for demodulation and is conveyed to the subscribers telephone station. It is only here that the demodulation is accomplished.

The drawing is a diagrammatic representation showing one embodiment of the invention.

Ts denotes a subscribers station which is connectcd to a terminal station belonging to a toll exchange E. The low-frequency speech currents liowing from the microphone Mi of station Ts are transferred through a low-pass iilter T1 and a two-wire line L to the exchange E and are there conveyed over a low-pass filter Ta to a modulator M1 where they serve to modulate an intermediate frequency of say 9 kilo cycles which is produced by a generator G. One of the side bands originating by such modulation is conveyed through a filter Fi of a second modulating stage M2 where it serves to modulate in company with an additional number of Wave bands a high carrier frequency of say 60 kilo cycles. This carrier frequency is used for long-distance transmission.

As regards the oncoming direction, the carrier frequency, being of the same order of frequency as that output from M2, is amplified by device A and is then demodulated by a demodulating means D. However, the resultant side bands of the appertaining intermediate carriers are not demodulated with the aid of a second modulating stage. VThey are merely supplied with the carrier from source G which is added to them by a device M3 to which output waves from D are conveyed over a filter F2. The carrier and appertaining side band are conveyed over a highpass lter H1 to the two-wire line L of station Ts. Here they are separated with the aid of a second high-pass filter H2 from the low-frequency currents, whereupon they are demodulated by a device D2. The product of demodulation, that is, the low-frequency currents originating in Dz, is reproduced by telephone receiver T.

In this Way the intermediate carrier already available is in a simple manner utilized for simplifying that part of the line arrangement which is located between exchange and subscribers station.

What is claimed is:

The combination of a toll exchange with a 'multi-channel carrier wave system terminating in this exchange, the incoming carrier waves each being modulated with a side-band of a signalmodulated intermediate frequency, means at said toll exchange to demodulate the incoming carrier waves on each channel and thereby derive the signal-modulated intermediate frequency side-band for each channel, a subscribers telephone station, a two-wire line for conveying said intermediate frequency side-band of one of said channels to said subscribers station, means at the toll exchange for adding to said transmitted side-band a carrier wave of said intermediate frequency, and means in the subscribers station for demodulating said added carrier wave and said transmitted nals.

ALFRED WIESSNER.

HERBERT NITZ.

side-band to produce the sig- 

